Not Applicable
Not Applicable
1. Field of Invention
This invention relates to heat exchangers, specifically to such exchangers as relate to collecting heat from the earth.
2. Description of Prior Art
Heat Pumps
Geothermal heat pumps, also called earth-coupled heat pumps, are commonly used to provide heating and cooling for conditioned spaces.
Heat Pump Technology
Originally, heat pumps used only the atmospheric air as a heat source or heat sink.
Because they are used to condition air inside a building, these are called air-to-air heat pumps.
In freezing temperatures, air-to-air heat pumps deteriorate in efficiency when operating in the heating mode. On the other hand, earth coupled heat pumps operating from a coil buried below the frost line show improved efficiencies in the heating mode, even in freezing weather.
At first earth coupled-coils were buried horizontally in trenches. Because deep earth temperatures are more stable, however, vertically drilled holes became an attractive alternative. Below 10 meters depth earth temperatures are constant year-round. Heat pumps operate more efficiently with a stable heat source.
But earth-coupled coils, whether horizontal or vertical, are costly to install. Horizontal systems require trenching equipment and sometimes even require a wide bucket backhoe. Trenches are a minimum of 1.2 meters deep. Vertical systems have the added disadvantage in that well drilling requires more specialized skills and equipment. Holes are typically 100 meters and more.
In either case, buried coils are susceptible to leaking, and are difficult or impossible to repair.
In addition, such coils are not readily installed in residential areas or in other places where the mess and the space requirements of trenching or drilling equipment cannot be tolerated.
Besides this, they have the added disadvantage in that once installed they cannot be moved; and the investment of drilling, trenching, or excavating, is irretrievably buried with the backfill.
Water source heat collection is also used. Closed loop systems often require permits and even engineering, as well as sufficient water to provide the necessary heat source or sink. Open loops have the additional disadvantage of coming under environmental review because they discharge water as a waste product. Sometimes this water is returned to an aquifer, thereby polluting the aquifer.
Other alternatives have been tried. Fluidized beds, buried containers, solar arrangements, and others. These have not succeeded.
Besides these, U.S. Pat. No. 6,251,179 to Allan (2001) discloses a cementitious grout for a bore hole; and Econar Energy Systems, www.econar.com, FAQ, page 3, teaches a slinky loop, coiled pipe, for a trench. While these improvements provide for shallower holes or shorter trenches, they still require drilling, trenching or other excavating.
Heat Exchanger Technology
The use of fins to enlarge the heat transfer area of heat exchangers is well established. Some common examples are the finned evaporators and condensers in home refrigerators; and the radiators, heaters, and air conditioners in automotive systems are other examples. All such exchangers are used to provide fluid-to-fluid heat exchange. Fluid-to-fluid heat exchangers provide an interface for heat transfer between fluids of differing temperatures. The heat transfer is primarily either by natural convection or by forced convection. Convective heat transfer is possible between fluids because of their nature. Solid, non-fluid substances, such as the earth, on the other hand, must transfer heat primarily by simple conduction.
Two solid, non-fluid, substances in thermal contact can provide their own interface for conductive heat transfer; but some type of heat exchange device needs to be provided if an exchange of heat between a solid and a fluid is desired. This solid-to-fluid heat exchanger must provide a conduit to contain the fluid, and to allow the fluid to pass through the exchanger. It must also provide a fin for convective heat transfer on the fluid side, and conductive heat transfer on the solid side.
At the same time, the fin must conform to both the shape of the flow of the fluid, as provided by the conduit, and the shape of the solid, e.g., the earth.
Finally, any non-conducting portion of the fin surface needs an insulating cover to minimize heat loss to any existing competing temperatures. Fluid-to-fluid heat exchangers do not provide an insulating cover. On the contrary, convective exchangers use all of the fin surface. This is because the fin extends entirely into the convective fluid where: there are no competing temperatures.
Typically, fluid-to-fluid exchangers feature a matrix of thin fins mechanically bonded, brazed, soldered, or welded to a conduit. This type of construction is complex and costly. In addition, this type of exchanger presents its fin edges, rather than its surface, to another surface when lying flat on the latter; and between the fins are gaps which are for full exposure to fluid flow, when these exchangers are used in fluid to-fluid applications. For conductive coupling to a solid, however, a fin must present its full conducting surface. Besides this, these present finned exchangers are premanufactured because they do not lend themselves to easy construction on the job. These premanufactured collectors are flat and therefore unsuitable for coupling to an irregular surface, such as naturally occurring rock. None of these finned exchangers is used for solid-to-fluid heat exchange, and in particular, none is used for earth coupled heat exchange.
In addition, no heat exchanger is available for direct coupling to the earth""s surface, without drilling, trenching, or other excavating; and none has an insulating cover.
Cold Region Technology
Geotechnical engineers, designing for permafrost conditions, gave us expressions to predict the thermal regime under insulated, heated, or cooled surfaces. Their focus was to avoid the disastrous effects that can occur with freezing and thawing under construction projects. No application was suggested for the use of these expressions to access deep earth temperatures for heat pumps.
Combination of Disciplines
No combination of these three technologies has been disclosed to provide a heat collector for geothermal heat pumps, without drilling, trenching, or other excavation.
This is because such a combination was outside of the focus of each of them.
Accordingly, the objects and advantages of the present invention are:
(a) to provide a collector which combines improved efficiency over air-to-air systems with economy of construction and installation;
(b) to provide a heat collector to collect geothermal heat directly from the surface of the earth; and which does not require drilling, trenching, excavating, or other special equipment or skills;
(c) to provide a collector for geothermal heat which does not require being buried in the earth;
(d) to provide a collector which can couple directly to the earth""s surface;
(e) to provide a collector which can access deep earth temperatures without drilling, trenching, or other excavation;
(f) to provide a collector which does not pollute;
(g) to provide a collector which is cheap and easy to replace or repair;
(h) to provide a collector which is at least as leakproof, and as reliable, as are present earth coupled systems;
(i) to provide a collector which is inexpensive and easy to install;
(j) to provide a heat collector which is portable;
(k) to provide a heat collector which is simple to construct, and which can be constructed on the job;
(l) to provide a heat collector having a fin which can be poured, rammed, or spread, to conform to the heat source surface;
(m) to provide a heat collector which does not require a use permit;
(n) to provide a heat collector having a fin which does not require brazing, soldering or welding;
(o) to provide a heat collector having a fin for solid-to-fluid heat exchange;
(p) to provide a heat collector which will operate at non-freezing temperatures without being buried, even over permafrost;
(q) to provide a heat collector having a cover to stabilize operating temperatures; and a fin to condense the conducting surface into a small area;
(r) to provide a heat collector with a stable heat source without drilling, excavating or trenching;
(s) to provide a heat collector to conduct heat by conduction from a non-fluid heat source, and
(t) to provide a heat collector which is insulated to minimize heat loss from its non-conducting fin surface;
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.
In accordance with the present invention a geothermal heat collector comprises a heat transfer conduit with heat transfer fluid therein, a fin in thermal contact with the conduit, and an insulating cover.